Sakurajima Volcano is located in northern part of Kagoshima Bay which is the southern extremity of Kyushu Island. So far as the origin is concerned Kagoshima Bay is considered as a submerged caldera, known by the name of Aira Caldera, and Sakurajima Volcano is the central cone of this caldera. Among many Japanese volcanoes Sakurajima Volcano is presently one of the most violent. Owing to the great eruption in January 1914 its name resounded all over the world. There are several papers written in european languages which reported this eruption.*
This volcano was built up in Pleistocene. It is a stratovolcano, consisting of basaltic andesite, and rises about 1, 100 meters above the sea and its coast line has a length of about 40 kilometers. Three craters on the summit line up from south to north.
Sakurajima is not single volcano but consists of two volcanic bodies, the northern and the southern. The former, called Kitadake Volcano, is the main and has a crater on the summit, measured about 600 meters in diameter and about 100 meters in depth. The latter, called Minamidake Volcano, overlaps the southern part of the former and has an active crater on the summit, being about 650 meters in diameter and about 230 meters in depth. Between these two craters there is a middle pit, called Nakadake, where a small crater on the summit exists.
Kitadake has been considered as a single volcano, the author, however, finds out that it should be divided into two volcanic bodies, the eastern and the western. The former is older and its summit still remains as crater wall. The latter, on the contrary, has a semicircle crater wall on it summit and at present is a dormant volcano. Between these crater walls a part of atrio of the older volcano is found. The contact zone of these two volcanoes appears as a reputured zone which extends on the northeastern mountainside of Kitadake Volcano. Great eruption as well as outflow of much lava happened along this line on the occasion of the eruption in An-ei Era, in the later half of the 18th century which may be the greatest eruption of this volcano throughout historical age. On the basis of the above-mentioned the author comes to conclusion that Kitadake is not a single but a composite volcano, consisting of the older and the younger volcanic bodies.
Nakadake's crater is somewhat elliptical, being about 300 meters in major diameter, about 800 meters in circumference and about 35 meters in depth. Presently it is also a dormant. Nakadake has been considered as a single volcano, the author, however, has the opinion that it may be divided into two bodies, the northern and the southern. The former is a small conic-shaped volcano whose summit as well as mountainside is everywhere covered thick by pumice and is a parasitic volcano of Kitadake. The latter, on the contrary, is characterized by its shallow pan-shape, measured only about ten or a few more meters in depth. The crater wall is preserved well where andesite layers can be observed. This is a parasitic volcano which erupted in close to the summit of Minamidake Volcano.
The above-mentioned is the author's observation on the landforms of Sakurajima Volcano, especially of its craters on the summit and neighborhood. Resulting from his field surveys the author concludes that Sakurajima Volcano is more complicated in structure than has ever been considered. Regarding the inner structure of this volcano the author expects of future researches.
